linux-kernel - Re: [PATCH kmod v2 3/4] kmod: Add config command to show compile time configuration as JSON

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Message-ID: <20230714165800.GO9196@kitsune.suse.cz>
Date:   Fri, 14 Jul 2023 18:58:00 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Nicolas Schier <nicolas@...sle.eu>
Cc:     linux-modules@...r.kernel.org, Takashi Iwai <tiwai@...e.com>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Michal Koutný <mkoutny@...e.com>,
        Jiri Slaby <jslaby@...e.com>, Jan Engelhardt <jengelh@...i.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH kmod v2 3/4] kmod: Add config command to show compile
 time configuration as JSON

On Fri, Jul 14, 2023 at 05:26:43PM +0200, Nicolas Schier wrote:
> On Wed, Jul 12, 2023 at 04:00:47PM +0200 Michal Suchanek wrote:
> > Show prefix (where configuration files are searched/to be installed),
> > module compressions, and module signatures supported.
> > 
> > Signed-off-by: Michal Suchanek <msuchanek@...e.de>
> > ---
> > v2: mention module signature in commit message
> > ---
> >  man/kmod.xml |  6 ++++++
> >  tools/kmod.c | 39 +++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 45 insertions(+)
> > 
> > diff --git a/man/kmod.xml b/man/kmod.xml
> > index 0706ad58c2cc..f992a500f836 100644
> > --- a/man/kmod.xml
> > +++ b/man/kmod.xml
> > @@ -71,6 +71,12 @@
> >            <para>Show the help message.</para>
> >          </listitem>
> >        </varlistentry>
> > +      <varlistentry>
> > +        <term><command>config</command></term>
> > +        <listitem>
> > +          <para>Show compile time options in JSON.</para>
> > +        </listitem>
> > +      </varlistentry>
> >        <varlistentry>
> >          <term><command>list</command></term>
> >          <listitem>
> > diff --git a/tools/kmod.c b/tools/kmod.c
> > index 55689c075ab1..5a13716955c1 100644
> > --- a/tools/kmod.c
> > +++ b/tools/kmod.c
> > @@ -37,9 +37,11 @@ static const struct option options[] = {
> >  };
> >  
> >  static const struct kmod_cmd kmod_cmd_help;
> > +static const struct kmod_cmd kmod_cmd_config;
> >  
> >  static const struct kmod_cmd *kmod_cmds[] = {
> >  	&kmod_cmd_help,
> > +	&kmod_cmd_config,
> >  	&kmod_cmd_list,
> >  	&kmod_cmd_static_nodes,
> >  
> > @@ -95,6 +97,43 @@ static const struct kmod_cmd kmod_cmd_help = {
> >  	.help = "Show help message",
> >  };
> >  
> > +static const char *compressions[] = {
> > +#ifdef ENABLE_ZSTD
> > +			"zstd",
> > +#endif
> > +#ifdef ENABLE_XZ
> > +			"xz",
> > +#endif
> > +#ifdef ENABLE_ZLIB
> > +			"gz",
> > +#endif
> > +			NULL
> > +};
> > +
> > +static int kmod_config(int argc, char *argv[])
> > +{
> > +	unsigned i;
> > +	printf("{\"prefix\":\"" PREFIX "\""
> > +			",\"module_signature\":["
> > +#ifdef ENABLE_OPENSSL
> > +			"\"PKCS#7\","
> > +#endif
> > +			"\"legacy\"]"
> > +			",\"module_compression\":[");
> > +	for(i = 0; compressions[i]; i++) {
> > +		printf("%s\"%s\"", i ? "," : "", compressions[i]);
> > +	}
> > +	printf("]}\n");
> > +
> > +	return EXIT_SUCCESS;
> > +}
> > +
> > +static const struct kmod_cmd kmod_cmd_config = {
> > +	.name = "config",
> > +	.cmd = kmod_config,
> > +	.help = "Show compile time options in JSON",
> > +};
> > +
> >  static int handle_kmod_commands(int argc, char *argv[])
> >  {
> >  	const char *cmd;
> > -- 
> > 2.41.0
> 
> If kmod could show selected configs without some (JSON) syntax
> around, it could simplify its proposed use in kbuild. E.g.:
> 
>     kmod config prefix 2>/dev/null
> 
> instead of
> 
>     kmod config &>/dev/null && kmod config | jq -r .prefix

Which would no longer hold for whole module directory:

      kmod config &>/dev/null && kmod config | jq -r .module_directory || echo /lib/modules

      vs

      kmod config module_directory &>/dev/null && kmod config module_directory || echo /lib/modules

Also JSON has standardized syntax for lists and users that can parse
JSON directly can load the whole configuration at once without several
calls to kmod config or pkg-config.

Thanks

Michal